Advertising Unreachable Links in OSPF
draft-ietf-lsr-ospf-ls-link-infinity-25

LSR Working Group                                                L. Gong
Internet-Draft                                                  W. Cheng
Updates: 5443, 6987, 8770 (if approved)                     China Mobile
Intended status: Standards Track                                  C. Lin
Expires: 15 September 2026                          New H3C Technologies
                                                               A. Lindem
                                                            Arrcus, Inc.
                                                                 R. Chen
                                                         ZTE Corporation
                                                           14 March 2026

                 Advertising Unreachable Links in OSPF
                draft-ietf-lsr-ospf-ls-link-infinity-25

Abstract

   OSPF Router Link State Advertisements (LSAs) use fixed-format
   encodings that always include advertised links in the default SPF
   (Shortest Path First) computation.  For non-default SPF computations,
   e.g., flexible algorithms as described in RFC 9350, advertised OSPF
   links are used in the default SPF computation even if this is not
   intended.  In order to advertise these links and not use them in the
   base SPF calculation, the metric LSLinkInfinity (0xffff) is used to
   specify that the link is unreachable.  If all OSPF routers in an OSPF
   area support this functionality and have advertised the capability
   via an area-scoped OSPF Router-Information LSA, then links advertised
   with a metric of LSLinkInfinity are considered unreachable.

   MaxReachableLinkMetric (0xfffe) is defined to provide backward
   compatible reachability in specifications that previously specified
   advertisement of MaxLinkMetric (0xffff).  This document updates RFC
   5443, RFC 6987, RFC 8379, and RFC 8770 with respect to the
   advertisement of MaxReachableLinkMetric (0xfffe) rather than
   MaxLinkMetric (0xffff).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 15 September 2026.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Case 1: Traffic Engineering . . . . . . . . . . . . . . .   4
     2.2.  Case 2: Flexible Algorithm  . . . . . . . . . . . . . . .   4
   3.  LSLinkInfinity-Based Solution . . . . . . . . . . . . . . . .   5
     3.1.  Unreachable Link Advertisement  . . . . . . . . . . . . .   5
     3.2.  Unreachable Link Backward Compatibility . . . . . . . . .   6
     3.3.  Stub Router Advertisement Backward Compatibility  . . . .   7
     3.4.  Label Distribution Protocol (LDP) IGP Synchronization
           Backward Compatibility  . . . . . . . . . . . . . . . . .   8
     3.5.  OSPF Graceful Link Shutdown Backward Compatibility  . . .   8
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
     4.1.  Configuration Parameters  . . . . . . . . . . . . . . . .   8
     4.2.  YANG Data Model . . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Tree for OSPF Functional Capability . . . . . . . . .   9
       4.2.2.  Tree for OSPF Advertising Unreachable Links . . . . .  10
       4.2.3.  IANA Module for OSPF Functional Capability Bits . . .  11
       4.2.4.  YANG Module for OSPF Functional Capability  . . . . .  13
       4.2.5.  YANG Module for OSPF Advertising Unreachable Links  .  17
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
     6.1.  Registering OSPF Router Functional Capability Bits  . . .  22
     6.2.  Registering YANG Modules  . . . . . . . . . . . . . . . .  22
     6.3.  IANA Module for OSPF Functional Capability Bits . . . . .  23

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   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  24
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  24
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  24
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   OSPF Router Link State Advertisements (LSAs) use fixed-format
   encodings that always include advertised links in the default SPF
   (Shortest Path First) computation.  For example, a link may be
   required for Traffic Engineering (TE) paths but not intended for hop-
   by-hop routing.  Another example is an OSPF link used exclusively by
   a Flexible Algorithm [RFC9350] but excluded from the default
   algorithm.

   In order to advertise these links as unreachable, the metric
   LSLinkInfinity (0xffff) is used to specify that the link is
   unreachable and OSPF routers supporting this specification will
   exclude the link from SPF calculations (subject to backward-
   compatibility, refer to Section 3.2).

   Stub Router Advertisement [RFC6987] defines MaxLinkMetric (0xffff) to
   indicate a router-LSA link should only be used for transit IP traffic
   as a last resort.  When an OSPF router supports the Unreachable Link
   capability defined in this document, OSPF Stub Router links are
   advertised as MaxReachableLinkMetric (0xfffe) rather than
   MaxLinkMetric (0xffff).  This document updates [RFC6987] and
   [RFC8770] with respect to the advertisement of MaxReachableLinkMetric
   rather than MaxLinkMetric.

   Similarly, Label Distribution Protocol (LDP) IGP Synchronization
   [RFC5443] specifies OSPF advertisement of MaxLinkMetric (0xffff) to
   indicate that while the OSPF adjacency is in FULL state, LDP has not
   been synchronized between the two neighbors and transit traffic is
   discouraged.  This document updates [RFC5443] with respect to the
   advertisement of MaxReachableLinkMetric rather than MaxLinkMetric.

   Finally, OSPF Graceful Link Shutdown [RFC8379] specifies OSPF
   advertisement of MaxLinkMetric (0xffff) to indicate that the OSPF
   link will be taken out of service and usage transit traffic is
   discouraged.  This document updates [RFC8379] with respect to the
   advertisement of MaxReachableLinkMetric rather than MaxLinkMetric.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Use Cases

2.1.  Case 1: Traffic Engineering

   A network topology is shown in Figure 1.  The OSPF link between Node
   A and E is only to be used for traffic engineering.  Since the OSPF
   link is advertised by default, it will be included in the base SPF
   calculation for the default topology and may be used for hop-by-hop
   routing in the default topology.

                               TE Link
                              ---------
                             /         \
                            /           \
                           A------C------E
                           |      |      |
                           |      |      |
                           |      |      |
                           B------D------F

                           Figure 1: Network Topology

2.2.  Case 2: Flexible Algorithm

   A network topology is shown in Figure 2.  The links between nodes A
   and B and between C and D are to be used exclusively for a flex-
   algorithm [RFC9350] devoted to specific traffic.  These links have an
   Extended Administrative Group (EAG) [RFC7308] attribute specifying
   the "Red" color.

                    ******
                   A------C------E
                   |*     |*     |
                   |*     |*     |        ******: "Red" link
                   |*     |*     |
                   B------D------F
                    ******

                    Figure 2: Network Topology

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   Flex-Algorithm 128 is enabled on Nodes A, B, C, and D, with an EAG
   rule including "Red" and the Metric-Type is designated to be a type
   other than the OSPF metric.  OSPF will compute routes for Flex-
   Algorithm 128 using these links.  The topology associated with Flex-
   Algorithm 128 is shown in Figure 3.

                               A******C
                               *      *
                               *      *
                               *      *
                               B******D

                 Figure 3: Topology of Flex-Algorithm 128

   The "Red" links are used by Flex-Algorithm 128 calculation.  However,
   these "Red" links are also included in the default algorithm
   calculation [RFC9350] since they are reachable.  Note that links used
   by the default algorithm are omitted from Figure 3 for clarity.

   If the OSPF metrics for all the "Red" links are advertised as
   unreachable, they will be excluded from the default SPF calculation
   as shown in Figure 4.  This allows the "Red" links from A to B and C
   to D to be used exclusively by the Flex-Algorithm 128 calculation.

                           A------C------E
                                         |
                                         |
                                         |
                           B------D------F

           Figure 4: Base SPF Topology Excluding Unreachable Links

3.  LSLinkInfinity-Based Solution

3.1.  Unreachable Link Advertisement

   This document specifies that if the OSPF metric of a link is
   advertised as LSLinkInfinity (0xffff), it MUST NOT be considered
   during the associated SPF computation.  This applies to both the
   Flex-Algorithm SPF [RFC9350] and the base SPF as long as
   LSLinkInfinity is specified for the OSPF metric.

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   While the interpretation of LSLinkInfinity is only required in the
   base topology as other topologies are optional [RFC4915], OSPF
   routers supporting this specification MUST consistently interpret
   LSLinkInfinity as unreachable during the associated SPF computation.
   Interpretation of LSLinkInfinity as unreachable is also applicable to
   Flex-Algorithm SPF computations [RFC9350] which use the OSPF link
   metric.

   An OSPF metric with LSLinkInfinity indicating a link is unreachable
   is applicable to the following TLVs/LSAs:

   *  The Router-LSA [RFC2328] [RFC5340]

   *  The Router-Link TLV of OSPFv3 E-Router-LSA [RFC8362]

3.2.  Unreachable Link Backward Compatibility

   Prior to this specification, OSPF treated links with an advertised
   metric of LSLinkInfinity as reachable [RFC2328].  Hence, partial
   deployment of this specification may result in routing loops due to
   inconsistent interpretation of LSLinkInfinity.  For example, in the
   network shown in Figure 5, link D-F is advertised with LSLinkInfinity
   (65535/0xffff).  Router B supports LSLinkInfinity as unreachable, but
   router A doesn't.  Router A considers link D-F as reachable, and the
   shortest path to F is A->B->D->F.  Router B considers link D-F as
   unreachable, and the shortest path to F is B->A->C->E->F.  As a
   result, A forwards the packets to B, but B returns them to A, which
   results in a routing loop.

          40000  40000      Traffic: A->F
        A------C------E       A considers link D-F as reachable
        |             |         A's shortest path: A->B->D->F
       5|             |5      B considers link D-F as unreachable
        |             |         B's shortest path: B->A->C->E->F
        B------D------F
            5    65535

     Figure 5: Inconsistent LSLinkInfinity Interpretation Causing Loops

   To provide backward compatibility, this document specifies that
   routers supporting LSLinkInfinity for unreachable links support
   advertisement of an area-scoped Router Information (RI) LSA with a
   Router Functional Capabilities TLV [RFC7770] including the following
   Router Functional Capability Bit. The value of the bit is controlled
   by configuration as specified in Section 4.1.

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                    +=====+==========================+
                    | Bit | Capabilities             |
                    +=====+==========================+
                    | TBD | Unreachable Link support |
                    +-----+--------------------------+

                                 Table 1

   OSPF Routers MUST NOT treat links with an advertised metric of
   LSLinkInfinity as unreachable unless all routers in the OSPF area,
   i.e., all routers with Router-LSAs in the area Link State Database
   (LSDB), have advertised this capability in an OSPFv2 Router
   Information Opaque LSA or an OSPFv3 Router Information LSA.  If all
   OSPF Routers in the area have advertised this capability, then links
   with an advertised metric of LSLinkInfinity MUST be treated as
   unreachable.  When the number of routers in the area not supporting
   the Unreachable Link Capability changes to 0 or from 0 to greater
   than 0, all OSPF routers in the area MUST recalculate their routes.

   In normal operation, it is possible that an area-scoped OSPF RI LSA
   will fail to reach all routers in an area in a timely manner.  For
   example, if a new router not supporting the the Unreachable Link
   Capability joins an area that previously only had OSPF routers
   advertising support of the Unreachable Link Capability, then it may
   take some time for the OSPF RI LSA to propagate to all routers.
   While it is propagating, the routers in the area will gradually
   detect the presence of a router that does not support the capability
   and will revert to treating links with MaxLinkMetric as being
   reachable.  During the propagation time, this inconsistency of
   MaxLinkMetric interpretation between OSPF routers can result in
   transient routing loops.

3.3.  Stub Router Advertisement Backward Compatibility

   Stub Router Advertisement [RFC6987] defines MaxLinkMetric (0xffff) to
   indicate a router-LSA link should not be used for transit traffic.

   When an OSPF router supports the Unreachable Link capability defined
   in this document, the OSPF stub router MaxLinkMetric (0xffff) MUST be
   updated to MaxReachableLinkMetric (0xfffe).  This document updates
   [RFC6987] and [RFC8770] with respect to the advertisement of
   MaxReachableLinkMetric rather than MaxLinkMetric.

   When an OSPF router supports [RFC6987] and the Unreachable Link
   capability defined in this document, it MUST support advertisement
   all its non-stub links with a link cost of MaxReachableLinkMetric
   (0xfffe).  Since MaxLinkMetric will not be used to indicate a link is
   unreachable unless all OSPF routers in the area support this

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   specification as specified in Section 3.2, all routers in the area
   will also support the usage of MaxReachableLinkMetric to discourage
   the usage of stub router links for transit traffic.  If there are any
   OSPF routers in the area that do not support the Unreachable Link
   capability, then all OSPF routers in the area will treat links
   advertised with a cost MaxLinkMetric as reachable (Section 3.2).

3.4.  Label Distribution Protocol (LDP) IGP Synchronization Backward
      Compatibility

   LDP IGP Synchronization [RFC5443] specifies OSPF advertisement of
   MaxLinkMetric (0xffff) to indicate that while the OSPF adjacency is
   in FULL state, LDP has not been synchronized between the two
   neighbors and transit IP traffic is discouraged.  When an OSPF router
   supports the Unreachable Link capability defined in this document,
   the usage of OSPF MaxLinkMetric (0xffff) to discourage usage of the
   link until LDP is "fully operational" MUST be updated to
   MaxReachableLinkMetric (0xfffe).  It is important to keep the link in
   the topology to allow IP traffic to use the link as a last resort in
   case of LDP packets between OSPF router loopbacks addresses or a
   network failure.  This document updates [RFC5443] with respect to the
   advertisement of MaxReachableLinkMetric rather than MaxLinkMetric.

3.5.  OSPF Graceful Link Shutdown Backward Compatibility

   OSPF Graceful Link [RFC8379] specifies OSPF advertisement of
   MaxLinkMetric (0xffff) to indicate that the link is going to be taken
   down and transit traffic is discouraged.  When an OSPF router
   supports the Unreachable Link capability defined in this document,
   the usage of OSPF MaxLinkMetric (0xffff) to discourage usage of a
   link prior to it being taken out of service MUST be updated to
   MaxReachableLinkMetric (0xfffe).  It is important to keep the link in
   the topology to allow IP traffic to use the link as a last resort
   prior to planned shutdown.  This document updates [RFC8379] with
   respect to the advertisement of MaxReachableLinkMetric rather than
   MaxLinkMetric.

4.  Operational Considerations

4.1.  Configuration Parameters

   Support of the Unreachable Link capability MUST be configurable.  The
   default MUST be to not advertise the capability, i.e., the functional
   capability in the area-scoped OSPF Router Information LSA is false.

   In some networks, the operator may still want links with maximum
   metric (0xffff) to be treated as reachable.  For example, when the
   cost of links is automatically computed based on the inverse of the

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   link's bandwidth and there is a mix of low-speed and high-speed
   links, the computation may result in the maximum metric.  Hence,
   implementations supporting this document and auto-costing MUST limit
   the maximum computed cost to MaxReachableLinkMetric (0xfffe).  An
   example of auto-costing would be to automatically set the link metric
   to be inversely proportional to the link bandwidth (refer to the
   auto-cost feature in the ietf-ospf.yang [RFC9129]).

4.2.  YANG Data Model

   This section defines three YANG [RFC7950] modules.  Module iana-ospf-
   functional-cap-bits defines the identities for OSPF Functional
   Capabilities as per the "OSPF Router Functional Capability Bits" IANA
   registry [IANA-OSPF-FC-Bits].  Module ietf-ospf-functional-capability
   and module ietf-ospf-unreachable-links can be used to configure and
   manage the usage of OSPF LSLinkInfinity for unreachable links as
   defined in this document, which augments the OSPF YANG data model
   [RFC9129] and the YANG Data Model for Routing Management [RFC8349].

   This document uses the graphical representation of data model per
   [RFC8340].

4.2.1.  Tree for OSPF Functional Capability

   The following shows the tree diagram of the module for OSPF
   Functional Capability:

   module: ietf-ospf-functional-capability
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area/ospf:interfaces/ospf:interface
               /ospf:database/ospf:link-scope-lsa-type
               /ospf:link-scope-lsas/ospf:link-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:ri-opaque/ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area/ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:ri-opaque/ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas

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               /ospf:as-scope-lsa/ospf:version/ospf:ospfv2
               /ospf:ospfv2/ospf:body/ospf:opaque/ospf:ri-opaque
               /ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area/ospf:interfaces/ospf:interface
               /ospf:database/ospf:link-scope-lsa-type
               /ospf:link-scope-lsas/ospf:link-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospf:router-information/ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv3
               /ospf:ospfv3/ospf:body/ospf:router-information
               /ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area/ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospf:router-information/ospf:router-capabilities-tlv:
       +--ro router-functional-capabilities
          +--ro functional-capability*   identityref

4.2.2.  Tree for OSPF Advertising Unreachable Links

   The following shows the tree diagram of the module for OSPF
   Advertising Unreachable Links:

   module: ietf-ospf-unreachable-links

     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area:
       +--rw unreachable-link-advertisement
          +--rw enabled?   boolean
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas
               /ospf:area/ospf:interfaces/ospf:interface:
       +--rw advertise-unreachable-link?   boolean

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4.2.3.  IANA Module for OSPF Functional Capability Bits

   IANA has created a registry titled "OSPF Router Functional Capability
   Bits" under the "Open Shortest Path First (OSPF) Parameters" registry
   group to identify OSPF Router Functional Capabilities.  Module iana-
   ospf-functional-cap-bits is an IANA-maintained module, which defines
   the identities for the OSPF Functional Capabilities as in the IANA
   "OSPF Router Functional Capability Bits" registry.

   This module is maintained by IANA and will be updated if and when
   there is any change to the registry.

   This document defines the initial version of the IANA-maintained YANG
   module for OSPF Router Functional Capabilities that mirrors the IANA
   "OSPF Router Functional Capability Bits" registry
   [IANA-OSPF-FC-Bits].  The latest version of this YANG module is
   available at TBD.

   Note to the RFC Editor: Please remove this module in the version to
   be published as RFC.

   This document defines the initial version of the IANA-maintained YANG
   module for OSPF Router Functional Capabilities that mirrors the IANA
   "OSPF Router Functional Capability Bits" registry
   [IANA-OSPF-FC-Bits].

   <CODE BEGINS> file "iana-ospf-functional-cap-bits@2026-01-28.yang"
   module iana-ospf-functional-cap-bits {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:"
             + "iana-ospf-functional-cap-bits";
     prefix iana-ospf-fc-bits;

     organization
       "Internet Assigned Numbers Authority (IANA)";
     contact
       "Internet Assigned Numbers Authority

        ICANN
        12025 Waterfront Drive, Suite 300
        Los Angeles, CA 90094-2536
        United States of America

        Tel:    +1 310 301 5800
        <mailto:iana@iana.org>";
     description
       "This YANG module defines the identities for OSPF Router
        Functional Capabilities.

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        This YANG module is maintained by IANA and reflects the 'OSPF
        Router Functional Capability Bits' registry.

        Copyright (c) 2026 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Revised BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This initial version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.

        The latest version of this YANG module is available at
        https://www.iana.org/assignments/yang-parameters.";

     revision 2026-01-28 {
       description
         "Initial version";
       reference
         "RFC XXXX: Advertising Unreachable Links in OSPF";
     }

     identity functional-capability {
       description
         "Base identity for OSPF Router Functional Capabilities. The
          functional capabilities are defined in IANA OSPF Router
          Functional Capability Bits registry.";
     }

     identity unreachable-link {
       base functional-capability;
       description
         "Indicates that the OSPF router is capable of advertising
          unreachable links.";
       reference
         "RFC XXXX: Advertising Unreachable Links in OSPF";
     }
   }
   <CODE ENDS>

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4.2.4.  YANG Module for OSPF Functional Capability

   The following is the YANG module for OSPF Functional Capability:

   <CODE BEGINS> file "ietf-ospf-functional-capability@2026-01-28.yang"
   module ietf-ospf-functional-capability {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:"
             + "ietf-ospf-functional-capability";
     prefix ospf-fc;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing Management
                    (NMDA Version)";
     }
     import ietf-ospf {
       prefix ospf;
       reference
         "RFC 9129: YANG Data Model for the OSPF Protocol";
     }
     import iana-ospf-functional-cap-bits {
       prefix iana-ospf-fc-bits;
       reference
         "RFC XXXX: Advertising Unreachable Links in OSPF";
     }

     organization
       "IETF Link State Routing (LSR) Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/lsr/>
        WG List:  <mailto:lsr@ietf.org>

        Author:   Yingzhen Qu
                  <mailto:yqu@futurewei.com>
        Author:   Acee Lindem
                  <mailto:acee.ietf@gmail.com>
        Author:   Liyan Gong
                  <mailto:gongliyan@chinamobile.com>
        Author:   Weiqiang Cheng
                  <mailto:chengweiqiang@chinamobile.com>
        Author:   Changwang Lin
                  <mailto:linchangwang.04414@h3c.com>
        Author:   Ran Chen
                  <mailto:chen.ran@zte.com.cn>";
     description
       "This YANG module defines the operational state for

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        Functional Capability in OSPF as defined in RFC 7770.

        Copyright (c) 2026 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.
        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Revised BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2026-01-28 {
       description
         "Initial version";
       reference
         "RFC XXXX: Advertising Unreachable Links in OSPF";
     }

     grouping router-functional-capabilities {
       description
         "Grouping for OSPF router capabilities TLV types.";
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
       container router-functional-capabilities {
         leaf-list functional-capability {
           type identityref {
             base iana-ospf-fc-bits:functional-capability;
           }
           description
             "List of functional capabilities. This list
              contains the identities for the functional
              capabilities supported by the router.";
         }
         description
           "OSPF Router Functional identity definitions.";
       }
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"

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           + "ospf:ospf/ospf:areas/ospf:area/"
           + "ospf:interfaces/ospf:interface/ospf:database/"
           + "ospf:link-scope-lsa-type/ospf:link-scope-lsas/"
           + "ospf:link-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/ospf:ri-opaque/"
           + "ospf:router-capabilities-tlv" {
       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "OSPFv2 Opaque Link-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:ri-opaque/ospf:router-capabilities-tlv" {
       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "OSPFv2 Opaque Area-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"

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           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:ri-opaque/ospf:router-capabilities-tlv" {
       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "OSPFv2 Opaque AS-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/"
           + "ospf:interfaces/ospf:interface/ospf:database/"
           + "ospf:link-scope-lsa-type/ospf:link-scope-lsas/"
           + "ospf:link-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information/"
           + "ospf:router-capabilities-tlv" {
       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "OSPFv3 Link-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information/"
           + "ospf:router-capabilities-tlv" {

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       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "OSPFv3 Area-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information/"
           + "ospf:router-capabilities-tlv" {
       when "derived-from-or-self(/rt:routing/"
          + "rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "OSPFv3 AS-Scoped Router-Information LSA Router
          Functional capabilities.";
       uses router-functional-capabilities;
       reference
         "RFC 7770: Extensions to OSPF for Advertising Optional
                    Router Capabilities";
     }
   }
   <CODE ENDS>

4.2.5.  YANG Module for OSPF Advertising Unreachable Links

   The following is the YANG module for OSPF Advertising Unreachable
   Links:

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   <CODE BEGINS> file "ietf-ospf-unreachable-links@2026-03-10.yang"
   module ietf-ospf-unreachable-links {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:"
             + "ietf-ospf-unreachable-links";
     prefix ospf-unreach-link;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing Management
                    (NMDA Version)";
     }
     import ietf-ospf {
       prefix ospf;
       reference
         "RFC 9129: YANG Data Model for the OSPF Protocol";
     }

     organization
       "IETF Link State Routing (LSR) Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/lsr/>
        WG List:  <mailto:lsr@ietf.org>

        Author:   Yingzhen Qu
                  <mailto:yqu@futurewei.com>
        Author:   Acee Lindem
                  <mailto:acee.ietf@gmail.com>
        Author:   Liyan Gong
                  <mailto:gongliyan@chinamobile.com>
        Author:   Weiqiang Cheng
                  <mailto:chengweiqiang@chinamobile.com>
        Author:   Changwang Lin
                  <mailto:linchangwang.04414@h3c.com>
        Author:   Ran Chen
                  <mailto:chen.ran@zte.com.cn>";
     description
       "This YANG module defines the configuration and operational
        state for Advertising Unreachable Links in OSPF as defined
        in RFC XXXX.

        Copyright (c) 2026 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Revised BSD License

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        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2026-03-10 {
       description
         "Initial version";
       reference
         "RFC XXXX: Advertising Unreachable Links in OSPF";
     }

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/ospf:ospf/"
           + "ospf:areas/ospf:area" {
       when "derived-from-or-self(../../../rt:type, 'ospf:ospfv2') or "
          + "derived-from-or-self(../../../rt:type, 'ospf:ospfv3')" {
         description
           "This augments the OSPF routing protocol when used.";
       }
       description
         "This augments OSPF protocol with unreachable link
          advertisement.";
       container unreachable-link-advertisement {
         leaf enabled {
           type boolean;
           default "false";
           description
             "Controls the interpretation of MaxLinkMetrc as
              unreachable and the advertisement of the unreachable
              link capability for the area. It is enabled when set
              to true and disabled when set to false.";
         }
         description
           "OSPF unreachable link advertisement parameters.";
       }
     }

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/ospf:ospf/"
           + "ospf:areas/ospf:area/ospf:interfaces/ospf:interface" {
       when "derived-from(/rt:routing/rt:control-plane-protocols/"

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          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2') or "
          + "derived-from(/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
         description
           "This augments the OSPF interfaces.";
       }
       leaf advertise-unreachable-link {
         type boolean;
         must "not(../advertise-unreachable-link = 'true' and "
            + "/rt:routing/rt:control-plane-protocols/"
            + "rt:control-plane-protocol/ospf:ospf/ospf:areas/"
            + "ospf:area/"
            + "ospf-unreach-link:unreachable-link-advertisement/"
            + "ospf-unreach-link:enabled = 'false')" {
           error-message "The interface cannot be advertised "
                       + "as unreachable (true) unless the "
                       + "unreachable-link-advertisement capability is "
                       + "enabled (true).";
           description
             "Ensures an interface isn't explicitly advertised as
              unreachable unless the OSPF instance level capability is
              enabled.";
         }
         default "false";
         description
           "Specifies that the link should be advertise with a metric
            of MaxLinkMetric (0xFFFF) in the default topology.";
       }
       description
         "Augment OSPF interfaces with anoption to advertise the link
          as unreachable.";
     }
   }
   <CODE ENDS>

5.  Security Considerations

   A compromised OSPF router could advertise changes to its Unreachable
   Link capability rapidly resulting in repeated route recalculations on
   routers in the area supporting this specification (Section 3.2).
   Hence, it is RECOMMENDED that routers supporting this specification
   also support the SPF back-off delay algorithm described in [RFC8405].

   The security considerations for [RFC2328], [RFC5340], [RFC6987], and
   [RFC7770] are also applicable to this protocol extension.

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   The ietf-ospf-unreachable-links YANG module and the ietf-ospf-
   functional-capability YANG module each define a data model that is
   designed to be accessed via YANG-based management protocols, such as
   NETCONF [RFC6241] and RESTCONF [RFC8040].  These YANG-based
   management protocols (1) have to use a secure transport layer (e.g.,
   SSH [RFC4252], TLS [I-D.ietf-tls-rfc8446bis], and QUIC [RFC9000]) and
   (2) have to use mutual authentication.

   The NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular NETCONF or RESTCONF users to a pre-
   configured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   There are a number of data nodes defined in the ietf-ospf-
   unreachable-links YANG module that are writable/creatable/deletable
   (i.e., "config true", which is the default).  All writable data nodes
   are likely to be sensitive or vulnerable in some network
   environments.  Write operations (e.g., edit-config) and delete
   operations to these data nodes without proper protection or
   authentication can have a negative effect on network operations.  The
   modification of these data nodes without proper protection can
   prevent interpretation of the OSPF LSLinkInfinity metric as
   unreachable or result in a link being advertised as unreachable.

      /ospf:ospf/ospf:areas/ospf:area/ospf-unreach-link:unreachable-
      link-advertisement/ospf-unreach-link:enabled

      /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      ospf-unreach-link:advertise-unreachable-link

   Some of the readable data nodes in the ietf-ospf-unreachable-links
   YANG module may be considered sensitive or vulnerable in some network
   environments.  Exposure of the OSPF unreachable link configuration
   may be useful in mounting a Denial-of-Service (DoS) attacks.  These
   are the readable data nodes:

      /ospf:ospf/ospf:areas/ospf:area/ospf-unreach-link:unreachable-
      link-advertisement/ospf-unreach-link:enabled

      /ospf:ospf/ospf:areas/ospf:area/ospf:interfaces/ospf:interface/
      ospf-unreach-link:advertise-unreachable-link

6.  IANA Considerations

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6.1.  Registering OSPF Router Functional Capability Bits

   This document defines a new bit in the registry "OSPF Router
   Functional Capability Bits" (https://www.iana.org/assignments/ospf-
   parameters/ospf-parameters.xhtml#router-functional-capability):

             +============+==================+===============+
             | Bit Number | Capability Name  | Reference     |
             +============+==================+===============+
             | TBD        | Unreachable Link | This document |
             +------------+------------------+---------------+

                                  Table 2

6.2.  Registering YANG Modules

   The IANA is requested to assign three new URIs from the IETF XML
   registry ([RFC3688]).  Authors are suggesting the following URIs:

   URI: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace

   URI: urn:ietf:params:xml:ns:yang:ietf-ospf-functional-capability
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace

   URI: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace

   This document also requests three new YANG module names in the YANG
   Module Names registry ([RFC6020]) with the following suggestion :

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   Name: iana-ospf-functional-cap-bits
   Maintained by IANA?  Y
   Namespace: urn:ietf:params:xml:ns:yang:iana-ospf-functional-cap-bits
   Prefix: iana-ospf-fc-bits
   Reference: RFC XXXX

   Name: ietf-ospf-functional-capability
   Maintained by IANA?  N
   Namespace: urn:ietf:params:xml:ns:yang:
              ietf-ospf-functional-capability
   Prefix: ospf-fc
   Reference: RFC XXXX

   Name: ietf-ospf-unreachable-links
   Maintained by IANA?  N
   Namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-unreachable-links
   Prefix: ospf-unreach-link
   Reference: RFC XXXX

6.3.  IANA Module for OSPF Functional Capability Bits

   This document defines the initial version of the IANA-maintained
   "iana-ospf-functional-cap-bits" YANG module (Section 4.2).  The most
   recent version of the YANG module is available from the "YANG
   Parameters" registry [IANA-YANG-Parameters].

   IANA is requested to add this note to the registry:

   |  New values must not be directly added to the "iana-ospf-
   |  functional-cap-bits" YANG module.  They must instead be added to
   |  the "OSPF Router Functional Capability Bits" registry in the "Open
   |  Shortest Path First (OSPF) Parameters" registry group
   |  [IANA-OSPF-FC-Bits].

   When a value is added to the "OSPF Router Functional Capability Bits"
   registry, a new "identity" statement needs to be added to the "iana-
   ospf-functional-cap-bits" YANG module.  The name of the "identity" is
   the lower-case name provided in the registry with all spaces replaced
   with “-“. The "identity" statement should have the following sub-
   statements defined:

     "base":          Contains 'functional-capability'.

     "description":   Contains the non-abbreviated OSPF capability bit
                      name from the registry.

     "reference":     Replicates the reference(s) from the registry with
                      the title of the document(s) added.

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   IANA is requested to add this note to [IANA-OSPF-FC-Bits]:

   |  When this registry is modified, the YANG module "iana-ospf-
   |  functional-cap-bits" must be updated as defined in RFC XXXX.

7.  Contributors

   The following individuals have contributed to this document:

      Mengxiao Chen
      New H3C Technologies
      China
      Email: chen.mengxiao@h3c.com

      Yanrong Liang
      Ruijie Networks Co., Ltd.
      China
      Email: liangyanrong@ruijie.com.cn

8.  Acknowledgments

   Thanks to Yingzhen Qu for providing the YANG model.

   Thanks to Dhruv Dhody for OPS Directorate review and comments.

   Thanks to Gunter van de Velde for review and comments.

   Thanks to Mohamed Boucadair for review and comments.

   Thanks to Mike Bishop, Mahesh Jethanadani, and Ketan Taulaulikar for
   review and comments.

9.  References

9.1.  Normative References

   [IANA-OSPF-FC-Bits]
              IANA, "OSPF Router Functional Capability Bits",
              <https://www.iana.org/assignments/ospf-parameters>.

   [IANA-YANG-Parameters]
              IANA, "YANG Module Names",
              <https://www.iana.org/assignments/yang-parameters>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC5443]  Jork, M., Atlas, A., and L. Fang, "LDP IGP
              Synchronization", RFC 5443, DOI 10.17487/RFC5443, March
              2009, <https://www.rfc-editor.org/info/rfc5443>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6987]  Retana, A., Nguyen, L., Zinin, A., White, R., and D.
              McPherson, "OSPF Stub Router Advertisement", RFC 6987,
              DOI 10.17487/RFC6987, September 2013,
              <https://www.rfc-editor.org/info/rfc6987>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

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   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,
              <https://www.rfc-editor.org/info/rfc8349>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [RFC8379]  Hegde, S., Sarkar, P., Gredler, H., Nanduri, M., and L.
              Jalil, "OSPF Graceful Link Shutdown", RFC 8379,
              DOI 10.17487/RFC8379, May 2018,
              <https://www.rfc-editor.org/info/rfc8379>.

   [RFC8405]  Decraene, B., Litkowski, S., Gredler, H., Lindem, A.,
              Francois, P., and C. Bowers, "Shortest Path First (SPF)
              Back-Off Delay Algorithm for Link-State IGPs", RFC 8405,
              DOI 10.17487/RFC8405, June 2018,
              <https://www.rfc-editor.org/info/rfc8405>.

   [RFC8770]  Patel, K., Pillay-Esnault, P., Bhardwaj, M., and S.
              Bayraktar, "Host Router Support for OSPFv2", RFC 8770,
              DOI 10.17487/RFC8770, April 2020,
              <https://www.rfc-editor.org/info/rfc8770>.

   [RFC9129]  Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
              "YANG Data Model for the OSPF Protocol", RFC 9129,
              DOI 10.17487/RFC9129, October 2022,
              <https://www.rfc-editor.org/info/rfc9129>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

9.2.  Informative References

   [I-D.ietf-tls-rfc8446bis]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8446bis-14, 13 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8446bis-14>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

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   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC7308]  Osborne, E., "Extended Administrative Groups in MPLS
              Traffic Engineering (MPLS-TE)", RFC 7308,
              DOI 10.17487/RFC7308, July 2014,
              <https://www.rfc-editor.org/info/rfc7308>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

Authors' Addresses

   Liyan Gong
   China Mobile
   China
   Email: gongliyan@chinamobile.com

   Weiqiang Cheng
   China Mobile
   China
   Email: chengweiqiang@chinamobile.com

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

   Acee Lindem
   Arrcus, Inc.
   United States of America
   Email: acee.ietf@gmail.com

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   Ran Chen
   ZTE Corporation
   China
   Email: chen.ran@zte.com.cn

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